Use `async` for benchmarks & remove Makefile

bench/Async.hs

-module Async where
-
-import Control.Concurrent (forkIO)
-import Control.Concurrent.MVar
-
-newtype Async a = Async (MVar a)
-
-async :: IO a -> IO (Async a)
-async action = do
-    mvar <- newEmptyMVar
-    _ <- forkIO $ do
-        x <- action
-        putMVar mvar x
-    pure (Async mvar)
-
-wait :: Async a -> IO a
-wait (Async a) = takeMVar a

bench/ChanBench.hs

 {-# LANGUAGE AllowAmbiguousTypes, ScopedTypeVariables, RankNTypes, TypeApplications #-}
 
+import Control.Concurrent.Async
 import Control.Monad
 import Data.Foldable (traverse_)
 import System.Environment
@@ -11,8 +12,6 @@ import Control.Concurrent.STM
 import Control.Concurrent.STM.TQueue
 import Control.Concurrent.STM.TBQueue
 
-import Async
-
 class Channel c where
     newc :: IO (c a)
     readc :: c a -> IO a

bench/Makefile

-GHC=ghc
-
-# Run chanbench for 4 different channel types, 3 different benchmarks
-all:
-	for i in CHAN TCHAN TQUEUE TBQUEUE; do $(GHC) -D$$i -O2 -fforce-recomp chanbench.hs -o chanbench-$$i; done
-	for i in 0 1 2; do echo; echo === test $$i ===; for j in CHAN TCHAN TQUEUE TBQUEUE; do printf "%-10s" $$j; time ./chanbench-$$j $$i 2000000; done; done

bench/stm-bench.cabal

@@ -13,8 +13,6 @@ description:
 benchmark chanbench
     type:             exitcode-stdio-1.0
     main-is:          ChanBench.hs
-    other-modules:
-        Async
-    build-depends:    base, stm, tasty, tasty-bench
+    build-depends:    base, stm, async, tasty, tasty-bench
     default-language: Haskell2010
     ghc-options:      -O2 -threaded -with-rtsopts=-N